Specialty ceramics are used as structural materials under high-temperature environment and excellent in resistance to heat and resistance to corrosion. These ceramics are being developed in wide applications including aeronautical, automotive, and electronic materials. However, ceramics are very difficult to machine. This is one impediment to practical usage of ceramics. One solution to this is to develop techniques for fabricating a complexly shaped article from small molded parts by joining. This is necessary to use ceramics as high-temperature materials in practice.
There have existed methods for joining ceramics together, using adhesive or solder. These methods need complex manufacturing steps. Further, the adhesive strength is not sufficient at high temperatures. Also, there exist methods for joining ceramics together by pressing them against each other using hot isostatic pressing or hot pressing through solid-phase diffusion. When these methods are employed, high adhesive strength is obtained at high temperatures, but a complex and large apparatus is needed. Further, the efficiency and the productivity are low, because the materials are totally heated.
One method of locally heating joining surfaces for joining ceramics together uses a laser or electron beam. When a laser beam is used, ceramics are externally heated and melted to join them together. Therefore, the internal strength is low, and the shape of the joining surfaces tends to deform. Further, only the oxide ceramics can be joined. Furthermore, it is difficult to accurately control the temperature. This creates a large temperature difference, causing cracks in the joining surfaces. In order to prevent the occurrence of the cracks, it is necessary to preheat the ceramics by other methods. Even if the occurrence of the cracks can be prevented, air bubbles remain in the joints, and crystal grains grow. In this way, a high reliability is not provided.
When metal workpieces are joined together, an electron beam is often used. However, it is difficult to join ceramics together with an electron beam, because ceramics are insulators. Even if ceramics can be joined together, cracks are produced by heat, and air bubbles remain in the same way as in the case using a laser beam. Hence, this method is not reliable, either.